Many people use access terminals, such as cell phones and personal digital assistants (PDAs), to communicate with cellular wireless networks. These access terminals and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1xRTT networks” (or “1x networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data connectivity.
More recently, service providers have introduced access terminals and wireless networks that communicate using a protocol known as EV-DO, which stands for “Evolution Data Optimized.” EV-DO networks, operating in conformance with industry specification IS-856, provide high rate packet-data service (including Voice over IP (VoIP) service) to access terminals using a combination of time-division multiplexing (TDM) on the forward link (from the network to access terminals) and CDMA technology on the reverse link (from access terminals to the network). Furthermore, some access terminals, known as hybrid access terminals or hybrid wireless access terminals, can communicate with both 1x networks and EV-DO networks.
In a typical cellular wireless network, an area is divided geographically into a number of cells and cell sectors, each defined by an RF radiation pattern from a respective antenna structure in the cellular wireless network. Within each cell sector, the RF radiation pattern provides an air interface over which access terminals may communicate with the cellular wireless network. In turn, the cellular wireless network may communicate with one or more other networks, such as the PSTN or a packet-switched network (e.g., the Internet). As such, when an access terminal is positioned within the coverage area of the cellular wireless network (e.g., in given cell sector), the access terminal can communicate with entities on the other networks via the cellular wireless network.
The RF air interface of any given cell sector in the cellular wireless network is typically divided into a plurality of channels for carrying communications between the access terminals and the cellular wireless network. For example, the RF air interface may include a plurality of forward-link channels, such as pilot channels, sync channels, paging channels, and forward-traffic channels, for carrying communications from the cellular wireless network to the access terminals. As another example, the RF air interface may include a plurality of reverse-link channels, such as access channels and reverse-traffic channels, for carrying communications from the access terminals to the cellular wireless network. However, the number of channels on the air interface, and thus the number of simultaneous communications the air interface can support, is limited by hardware and/or protocol constraints. As such, cellular wireless networks often try to conserve the limited supply of channels by assigning them on an as-needed basis.
When the cellular wireless network receives a request to set up a communication with a given access terminal (either from the access terminal itself, or another access terminal wishing to communicate with the given access terminal), the cellular wireless network may assign the given access terminal a traffic channel in the given cell sector by (i) reserving an available traffic channel for communication with the given access terminal, and (ii) sending the given access terminal a channel assignment message identifying the reserved traffic channel. Thus, a traffic channel assignment (TCA) message is typically used to notify an access terminal of the traffic channel that is assigned to the access terminal. As such, when an access terminal attempts to establish a connection to an access network, the access network may select a traffic channel for the access terminal, and send the access terminal a TCA message that identifies the selected traffic channel. Upon receipt of the channel assignment message, the given access terminal may acquire the identified traffic channel, and communication over the traffic channel may begin shortly thereafter.
Furthermore, when an access terminal receives a TCA message and tunes to the assigned traffic channel, the access terminal may notify the access network by sending a traffic-channel complete (TCC) message to the access network. Thus, if the access network does not receive a TCC complete message within a predetermined period of time, the access network assumes that the TCA message has not been properly received, and accordingly, re-transmits the TCA message to the access terminal. The access network then repeats this process until a TCC complete message is received, or until it reaches a predetermined number of attempts to transmit the TCA message (which in current networks is typically three).